Gypsum fiber board panels have been used in the construction industry to form the interior and exterior walls of residential and/or commercial structures. However, a drawback of such conventional panels is that they do not have sufficient flexural toughness to the extent that such panels may be comparable to wood-based panels such as plywood or oriented strand board (OSB).
Building structures during their lifetimes are subjected to a variety of impact loads (e.g., hail damage, or damage from objects hurled at the buildings due to tornados or hurricanes). Not all building sheathing panels are sufficiently tough to withstand such impact loads. Where it is necessary to demonstrate impact load resistance, the sheathing panels are measured to determine the impact the panel can resist without failure.
Flexural toughness as characterized in this specification is measured as equal to the total area under the flexural load versus deflection curve for a specimen loaded in three-point bending.
One example of flexural toughness is measured as the total area under the load versus deflection curve for a flexural specimen loaded in a 3-point bending according to ASTM D1037 test method.
Wood-based panels achieving significant flexural toughness usually are plywood or oriented strand board (OSB), which consist of wood veneers or large chips that are glued together. These panels can provide flexural toughness, but each is combustible and in many cases other than marine plywood, these panels are not durable when exposed to water. A panel made of hydraulic cement will resist water, but is much heavier than the wood panels. It is believed that there is no panel currently available at a comparable cost which can provide the flexural toughness of the present invention, while avoiding the deficiencies of plywood or OSB panels.
Furthermore, the need for gypsum fiber panels configured to behave in the construction environment similar to plywood and OSB means the panels are nailable and can be cut or worked using conventional saws and other conventional carpentry tools.
The panel should be capable of being cut with the circular saws used to cut wood. The panel should also be capable of being fastened to framing with nails or screws.
The panel should be dimensionally stable when exposed to water, i.e., it should expand as little as possible, preferably less than 0.1% as measured by ASTM C 1278. The Standard specification for some gypsum fiberboard panels is listed at 5% moisture uptake in a 2 hour soak, although other gypsum fiber board panel products can have as much as 10% moisture uptake in a 2 hour soak test. The panel should not be biodegradable or subject to attack by insects or rot. However, the panel should provide a bondable substrate for exterior finish systems.
The flexural strength of a 0.5 inch (12.7 mm) thick gypsum fiberboard panels (GFP) having a density of about 714 kg/m3 (50 lb/ft3) to about 1000 kg/m3 (70 lb/ft3) is at least 5.2 MPa (750 psi), and preferably greater than 6.9 MPa (1000 psi) as measured by the ASTM D1037 test.
It should be evident that the currently available gypsum fiber based and wood-based products and composites meet some, but not all, of the above performance characteristics. In particular, there is a need for improved gypsum fiber based panels that are lightweight having improved flexural toughness and which exceed the capability of the currently-used gypsum fiber board and wood-based by providing non-combustibility and water durability.
Although glass fibers have been used to reinforce gypsum board and gypsum fiber board, other fibers have been suggested to reinforce gypsum board, such as metal fibers, wood or paper fibers, carbon fibers, or polymer fibers.
U.S. Pat. No. 5,320,677 to M. Baig, incorporated herein by reference in its entirety, discloses a composite gypsum/wood fiber (GWF) material product and a process for forming the product in which a dilute slurry of gypsum particles and cellulosic fibers are heated under pressure to convert the raw gypsum to calcium sulfate hemihydrate by calcining the gypsum in the presence of wood fibers. The dissolved calcium sulfate wets the voids in the fiber and the resulting hemihydrate eventually forms crystals in situ in the voids of the cellulose fiber. However, it would be desirable to further improve the GWF to reduce the density and improve the flexibility of the panel, reduce the amount of unreacted hemihydrate that can not be readily rehydrated to gypsum in the GWF production process, and reduce the setting time of the panel while significantly reducing the amount of steam energy required to calcine the gypsum to calcium sulfate hemihydrate.
U.S. Pat. No. 6,508,895 to Lynn et al, incorporated herein by reference, discloses a paperless gypsum/fiberboard which has improved impact resistance compared to gypsum/fiberboard by use of a process wherein a multilayer gypsum/fiber board is formed having a flexible mesh, preferably fiberglass mesh embedded in the backside of the board, to provide improved impact resistance. In the process, the mesh is fed into the forming area of the panel before the panel is pressed prior to drying. Optionally, a second layer of mesh can be embedded in the top layer of the gypsum/fiberboard.
U.S. Pat. No. 4,199,366 A to Schaefer et al., incorporated herein by reference, discloses a fiber-reinforced cement material having short polyvinyl alcohol fibers in an amount of at least 2 volume % based on the total volume of the material. These fibers have an elongation at break of between about 4 and 8% and a modulus of more than 130 g/dtex. A process for the preparation of the material is also disclosed.
U.S. Pat. No. 4,306,911 A to Gordon et al., incorporated herein by reference, discloses a method for the production of a fiber-reinforced hydraulically obtained setting material.
U.S. Pat. No. 4,339,273 A to Meier et al., incorporated herein by reference, discloses a process for producing a fiber-reinforced, hydraulically setting composition, the composition produced, and the use thereof.
U.S. Pat. No. 5,298,071 A to Vondran, incorporated herein by reference, discloses a fiber-hydratable cement composition comprising a uniform dispersion interground fiber in hydratable cement powder.
U.S. Pat. No. 5,817,262 A to Englert, incorporated herein by reference in its entirety, discloses a process for making a gypsum wood fiber board with improved moisture resistance through addition of an aqueous siloxane emulsion to the calcined gypsum and wood fiber slurry at a temperature above the point at which the hemihydrate will rehydrate to gypsum.
U.S. Pat. No. 6,010,596 to Song, incorporated herein by reference in its entirety, discloses a process for making a moisture resistant gypsum wood fiberboard by adding a wax emulsion to calcined gypsum and wood fiber slurry before the calcium sulfate hemihydrate will rehydrate to gypsum.
U.S. Pat. No. 6,221,521 B1 to Lynn, incorporated herein by reference in its entirety, discloses a three layer paperless fiber reinforced gypsum/fiberboard product that is non-combustible and which uses no more than 3% by weight organic material in its core layer and 10-30% paper reinforcing fiber added to calcined gypsum in its surface layers.
U.S. Pat. No. 6,268,042 B1 to Baig, incorporated herein by reference in its entirety, discloses a high strength low density fiber board panel for use in furniture made from mineral wool, lightweight aggregate, 20 to 35% cellulose fiber, binder and up to 23% gypsum solids.
U.S. Pat. No. 6,406,779 B1 to Carbo et al., incorporated herein by reference in its entirety, discloses a paperless gypsum/fiberboard made with calcined gypsum and added cellulose fiber with improved surface characteristics by addition of a heat curable primer comprising an aqueous emulsion of a film forming polymeric material.
U.S. Pat. No. 6,508,895 B2 to Lynn et al., incorporated herein by reference in its entirety, discloses a paperless multi-layered gypsum fiberboard with improved impact resistance that has a fiberglass mesh embedded in its back side.
U.S. Pat. No. 6,531,210 B2 and U.S. Pat. No. 7,056,460 to Englert, incorporated herein by reference in its entirety, discloses a process for preparing an improved gypsum/wood fiberboard by addition of a stable methylenediphenyldiisocyante emulsion to an aqueous slurry of calcined gypsum and wood fiber just prior to the slurry being fed to the headbox in the process described in U.S. Pat. No. 5,558,710 A, above.
U.S. 2005/0161853 to Miller et al., incorporated herein by reference in its entirety, discloses an improved process for calcining gypsum and cellulose fiber in the manufacture of gypsum/cellulose fiber products by addition of crystal modifiers prior to heating to reduce the time and temperature necessary to complete calcination or to increase the aspect ratio of the acicular crystals formed during calcination process.
US. 2006/0243171 to Yu et al., incorporated herein by reference in its entirety, discloses a wet gypsum accelerator comprising an organic phosphonic compound, a phosphate-containing compound and mixtures thereof for increasing the rehydration of calcined gypsum.
US2007/0056478 to Miller et al., incorporated herein by reference in its entirety, discloses an improved method for making a water resistant gypsum fiberboard that comprises adding a silicone compound and magnesium oxide to a calcined slurry of calcium sulfate hemihydrate and cellulose fiber after the calcination step and before dewatering the slurry to form a filter cake.